Push pull current sources find use in circuit design wherever the difference between opposing current signals is a preferred way to transmit a control signal. The sum of the opposing currents is constant, with the, difference between them proportional to the value of the control signal. Some of the applications for which such current sources are used include providing gain control for Gilbert gain cells and providing a precise offset current into a push-pull DC amplifier.
Conventional push-pull current sources suffer from several drawbacks. For one, their designs tend to be so complex that they are not easily adapted to different circuit environments. For another, the current signals lose their linear relationship to the control signal at its extreme values.
For example, U.S. Pat. No. 4,528,515 to Gross discloses a high-frequency differential amplifier whose linear relationship between its input voltage signal and output current signal is poor at the extreme values of the input signal.